sc16is7xx: Update status lines in single call

RTS, DTR and LOOP bits can be updated in a single MCR register update.
This reduces the number of (slow) SPI/I2C bus transactions.

Signed-off-by: Lech Perczak <l.perczak@camlintechnologies.com>
Signed-off-by: Tomasz Moń <tomasz.mon@camlingroup.com>
Link: https://lore.kernel.org/r/20220221105618.3503470-3-tomasz.mon@camlingroup.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>